This invention relates to slides for use in microscopic examination of biological fluid.
It is known that plates, called slides, have been used in the microscopic examination of biological fluid, such as urine, blood, and spinal fluid, for the purpose of carrying out a computation of elements present in a predefined sample. The slides are constituted by two plates of transparent plastic material, one for a floor and one for a covering, which define a plurality of wells in their interiors. The wells are filled by capillarity with drops of the biological fluid which are deposited on the slide itself.
On the floor of each well are formed computation chambers, in each of which is contained an accurate volume of biological fluid to be examined. These computation chambers are obtained by means of reliefs which are formed from the floor of the well towards the covering or roof.
In reference to the trajectory of the reliefs it is possible to obtain quadrilateral or circular computation chambers, depending on whether the reliefs have a rectilinear direction so as to form grids or have a circular direction so as to form circles which are reciprocally separated. By way of example of the first type of computation chamber, the European Patent Publication No. 326,349 A2 describes a slide made of plastic material in which computation chambers in wells are defined by a grid pattern made up of symmetrical lines. The symmetrical lines have a width of between about 0.008 mm and 0.05 mm, and extend upwardly from the floor of the well preferably for 0.008 mm and the minimal area for the reading of each chamber has a floor of 0.111 mm.
Also by way of example, with respect to the second type of a computation chamber, the slides produced by the company Kima have reliefs of a width between 0.005 mm and 0.05 mm. The relief forms a circular computation chamber having as the floor a circle of internal diameter 0.376 mm.
The reliefs or grids define computation chambers, preferably arranged 3xc3x973, and the total internal surface of all the chambers is 1 mm2. In order to obtain reliefs of millesimal dimensions, the production of these types of slides from plastic material requires the use of molds provided with engraved marks and impressions which are of microscopic value, well defined, and made by means of special machines for the removal of chips, by electroerosion, or with other processes known in the art.
In fact, by means of constructions known up to the present, observations with an optical microscope for measuring small particles in a fluid sample are often inaccurate, because in conventional reliefs the optical lines which correspond respectively to the line of the vertex and to the line of the bottom of the relief are subject to confusion due to the inclination of the wall of the relief.
This fact causes an error in the reading or in the computation of small particles because it is difficult to examine the small particles which remain adhering to the inclined walls. There is also a discrepancy in reading the values of areas measured on the upper plane of the computation chamber (corresponding to the relief), and areas measured a the bottom of the computation chamber. This error is further increased due to the fact that it has heretofore been impossible to provide reliefs with inclined walls which are perfectly uniform along the entire computation chamber.
The present invention relates to slides in which computation chambers present in wells are defined by reliefs which protrude from the bottom of the chambers. The reliefs are preferably rectilinear or circularxe2x80x94a profile easily achievable with machines. The reliefs define precise lateral walls of the computation chamber so as to measure accurately the volume of the chamber.
The invention provides slides comprising reliefs defining computation chambers which are sectioned along a plane perpendicular to the bottom of the well. The relief has a section with a profile shaped as a polygon having at least one right angle. The right angle is defined by the bottom of the computation chamber and the internal lateral wall of the computation chamber.
The invention further provides that the lateral wall of the computation chamber has its upper extremity constituted by a corner which is a part of the polygon which defines the relief. The lateral wall has an internal angular opening of 90 degrees at the most and is rounded with a radius of curvature at the most 0.002 mm.
In operation, the preferred form of the reliefs has a rectangular trapezium or a rectangular triangle section. The embodiments essentially better define the separation between the area which constitutes the computation chamber and the surrounding area which separates reciprocally the plurality of the chambers.